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Area of an equilateral triangle
The area of an equilateral triangle (all sides congruent) can be found using the formula
where s is the length of one side of the triangle.
Try this Drag the orange dots on each vertex to reshape the triangle. The formula shown will recalculate the area using this method.

When you know all three sides of a triangle, the usual way to find the area is to use Heron's Formula. But in the case of equilateral triangles, where all three sides are the same length, there is a simpler formula:

where
s is the length of any side of the triangle.

Methods for finding triangle area

If you know: Use this
Base and altitude "Half base times height" method
All 3 sides Heron's Formula
Two sides and included angle Side-angle-side method
x,y coordinates of the vertices Area of a triangle- by formula (Coordinate Geometry)
Area of a triangle - box method (Coordinate Geometry)
The triangle is equilateral Area of an equilateral triangle
Try this
  1. In the figure above, click on "hide details"
  2. Drag the vertices of the triangle to make a new size triangle
  3. Calculate the are using this method
  4. Click "show details" to verify your answer

Related triangle topics

General

Perimeter / Area

Triangle types

Triangle centers

Congruence and Similarity

Solving triangles

Triangle quizzes and exercises

(C) 2009 Copyright John Page